DISCUSSION ON THE CORRELATION OF THE XUJIAHE FORMATION IN SICHUAN BASIN

According to the basin evolution and tion of the lateTriassic sedimentary sources, we believe that the late Triassic is represents an interval during which the continental margin basin controlled by Bayankala sea switched to a West Sichuan foreland basin controlled by Longmen Mountains which was napping and uplifting. The transition is represented by the Anxian tectonic movement between the third and fourth members of the Xujiahe Formation. On the basis of drilling data, outcrop observation, and stratigraphic correlation,we think that the second and third members of the Xujiahe Formation are mainly developed in the north part of the West Sichuan Basin,as typified by the Yazihe area. Affected by the Anxian Tectonic Movement,the third member of the Xujiahe Formation was eroded in the southern part of the basin; the thickness of this member gradually decreases from the north to the Dayi structure in the south,and it is completely missing in the Pingluoba structure where the second member is in direct contact with the fourth member of the Xujiahe Formation. The second and third members of the Xujiahe Formation thin eastward from the western Sichuan Basin,and is missing in the middle Sichuan Basin. The Xujiahe Formation which in the middle, south and east parts of Sichuan Basin are equivalent to the fourth and fifth members of the Xujiahe Formation in the western Sichuan Basin.